Seismic acquisition using Radar Interferometry

Abstract

We have investigated the feasibility of seismic acquisition using radar interferometry. To this end we first calculated a seismic surface response for a representative subsurface. The outcome was used as input in a typical InSAR processing technology on synthetic InSAR data and compared with the results from an experiment carried out earlier.

We calculated the surface response with the spectral element method. It represents well the waveforms of direct P- and S-waves, reflections PnP, S1S and P1S, and Rayleigh waves as function of space and time. To achieve realistic amplitudes, however, the modelled waves had to be multiplied with a factor 1000. With these waves, we found that InSAR can very well be applied to 10 GHz radars to measure deviations in distance between radar and reflectors (DeltaR) in the orders of 10^{-9} m to 10^{-1} m. With the presence of noise, however, an uncertainty in DeltaR is introduced. At a high signal to noise ratio (SNR) of 10^{7} (i.e., 70 dB), uncertainties in DeltaR of 10^{-6} m were found. We expect for such large SNR, seismic deformations can be measured using InSAR. Indeed, in an optimal setting with optimal pulse characteristics and an optimal amount of reflectors, SNR of the raw data can be increased with a factor 10^{5} and an SNR of 10^{2} for the raw data then would suffice.

We found that direct P- and S-waves, and reflections S1S and P1S can be observed well, both from a stationary and an oscillating radar. Noisy radar movements in the frequency range of the seismic response, however, need to be suppressed physically, with a physical low pass filter. Then, in the processing, a simple high pass filter results in the DeltaR due to the seismic displacements.

A new assessment of older experimental data resulted in a DeltaR uncertainty larger than 5*10^{-5}, with the measured DeltaR mainly representing the radar motion. New experiments should therefore account for the lessons learnt in the present study. We then expect that the application of radar interferometry to seismic acquisition is feasible.